Using sensor data from an intracardially implanted medical device to influence operation of an extracardially implantable cardioverter

ABSTRACT

A medical system for sensing and regulating cardiac activity of a patient may include a cardioverter that is configured to generate and deliver shocks to cardiac tissue and a leadless cardiac pacemaker (LCP) that is configured to sense cardiac activity and to communicate with the cardioverter. The cardioverter may be configured to detect a possible arrhythmia and, upon detecting the possible arrhythmia, may send a verification request to the LCP to help conform that the possible arrhythmia is occurring. The LCP, upon receiving the verification request from the cardioverter, may be configured to activate one or more of a plurality of sensors to attempt to help confirm that the possible arrhythmia is occurring.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/397,905 filed on Sep. 21, 2016, the disclosureof which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to implantable medical devices,and more particularly, to systems that use an intracardially implantedmedical device such as a leadless cardiac pacemaker for monitoring,pacing and/or defibrillating a patient's heart.

BACKGROUND

Implantable medical devices are commonly used today to monitor a patientand/or deliver therapy to a patient. For example and in some instances,cardiac pacing devices are used to treat patients suffering from variousheart conditions that may result in a reduced ability of the heart todeliver sufficient amounts of blood to a patient's body. Such heartconditions may lead to slow, rapid, irregular, and/or inefficient heartcontractions. To help alleviate some of these conditions, variousmedical devices (e.g., pacemakers, cardioverters, etc.) can be implantedin a patient's body. Such devices may monitor and in some cases provideelectrical stimulation (e.g. pacing, defibrillation, etc.) to the heartto help the heart operate in a more normal, efficient and/or safemanner.

SUMMARY

This disclosure generally relates to medical devices, and moreparticularly, to systems that use sensor data from an intracardiallyimplanted medical device such as a leadless cardiac pacemaker toinfluence operation of an extracardially implantable cardioverter suchas a subcutaneous implantable cardioverter defibrillator (SICD). In anexample of the disclosure, a medical system for sensing and regulatingcardiac activity of a patient includes a cardioverter that is configuredto generate and deliver anti-arrhythmic therapy to cardiac tissue, and aleadless cardiac pacemaker (LCP) that is configured to sense cardiacactivity and to communicate with the cardioverter. The cardioverter maybe configured to detect a possible arrhythmia and, upon detecting thepossible arrhythmia, may send a verification request to the LCPsoliciting verification from the LCP that the possible arrhythmia isoccurring. The LCP, upon receiving the verification request from thecardioverter, may be configured to use signals from one or more of aplurality of sensors of the LCP to attempt to confirm that the possiblearrhythmia is occurring.

The LCP may be configured to send a confirmation response to thecardioverter if the LCP confirms that the possible arrhythmia isoccurring. In some cases, the cardioverter may be configured to generateand deliver a therapy to cardiac tissue if the LCP confirms that thepossible arrhythmia is occurring and to inhibit delivery of a therapy tocardiac tissue if the LCP did not confirm that the possible arrhythmiais occurring.

Alternatively or additionally to any of the embodiments above, at leastsome of the plurality of sensors of the LCP include a first sensor thatwhen activated consumes a first level of power and a second sensor thatwhen activated consumes a second level of power, wherein the secondlevel of power is higher than the first level of power. Upon receivingthe verification request from the cardioverter, the LCP may beconfigured to initially activate the first sensor to attempt to confirmthat the possible arrhythmia is occurring. If the LCP confirms that thepossible arrhythmia is occurring using the first sensor, the LCP may beconfigured to send the confirmation response to the cardioverter. If theLCP does not confirm that the possible arrhythmia is occurring using thefirst sensor, the LCP may be configured to activate the second sensor toattempt to confirm that the possible arrhythmia is occurring. If the LCPconfirms that the possible arrhythmia is occurring using the secondsensor, the LCP may be configured to send the confirmation response tothe cardioverter.

Alternatively or additionally to any of the embodiments above, the LCPfurther includes a third sensor that when activated consumes a thirdlevel of power, wherein the third level of power is higher than thesecond level of power. If the LCP does not confirm that the possiblearrhythmia is occurring using the second sensor, the LCP may beconfigured to activate the third sensor to attempt to confirm that thepossible arrhythmia is occurring. If the LCP confirms that the possiblearrhythmia is occurring using the third sensor, the LCP may beconfigured to send the confirmation response to the cardioverter.

Alternatively or additionally to any of the embodiments above, the LCPmay include at least a first electrode and a second electrode, and thefirst sensor comprises detecting electrical cardiac activity via thefirst electrode and the second electrode.

Alternatively or additionally to any of the embodiments above, thesecond sensor may be configured to detect heart sounds.

Alternatively or additionally to any of the embodiments above, thesecond sensor may include an accelerometer disposed relative to the LCP.

Alternatively or additionally to any of the embodiments above, thesecond sensor may include a pressure sensor disposed relative to theLCP.

Alternatively or additionally to any of the embodiments above, the thirdsensor may include an optical sensor.

Alternatively or additionally to any of the embodiments above, theverification request from the cardioverter may include an indication ofseverity of the possible arrhythmia, and if the indication of severityexceeds a threshold severity level, the LCP may be configured toconcurrently activate two or more of the plurality of sensors and to usethe concurrently activated two or more of the plurality of sensors toattempt to confirm that the possible arrhythmia is occurring in anexpedited manner.

Alternatively or additionally to any of the embodiments above, the LCPmay be configured to concurrently activate two of the plurality ofsensors upon receiving the verification request from the cardioverterand to examine both a signal from a first sensor of the plurality ofsensors and a signal from a second sensor of the plurality of sensors toattempt to confirm that the possible arrhythmia is occurring.

In another example of the disclosure, a leadless cardiac pacemaker (LCP)that is configured for implantation relative to a patient's heart and tosense electrical cardiac activity and deliver pacing pulses whenappropriate includes a housing, a first electrode that is securedrelative to the housing and a second electrode that is secured relativeto the housing and is spaced from the first electrode. A controller maybe disposed within the housing and operably coupled to the firstelectrode and the second electrode such that the controller is capableof receiving, via the first electrode and the second electrode,electrical cardiac signals of the heart. In some cases, the firstelectrode and the second electrode form a first sensor that, whenactivated, consumes a first level of power. The LCP may include a secondsensor that is disposed relative to the housing and operably coupled tothe controller, the second sensor, when activated, consumes a secondlevel of power that is higher than the first level of power. Acommunications module may be disposed relative to the housing andoperably coupled to the controller, the communications module configuredto receive a verification request from a cardioverter to confirm that apossible arrhythmia is occurring. Upon receipt of the verificationrequest from the cardioverter via the communications module, thecontroller may be configured to initially sense cardiac activity usingthe first sensor to help confirm that the possible arrhythmia isoccurring while the second sensor is in a lower power state. In somecases, if the possible arrhythmia is not confirmed using the firstsensor, the controller may be configured to activate the second sensorfrom the lower power state to a higher power state, and then sensecardiac activity using the second sensor to help confirm that thepossible arrhythmia is occurring.

Alternatively or additionally to any of the embodiments above, thesecond sensor may include an accelerometer or a pressure sensor.

Alternatively or additionally to any of the embodiments above, the LCPmay further include a third sensor that is disposed relative to thehousing and operably coupled to the controller, the third sensor, whenactivated, consumes a third level of power that is higher than thesecond level of power. If the possible arrhythmia is not confirmed usingthe second sensor, the controller may be configured to activate thethird sensor from the lower power state to a higher power state, andthen attempt to confirm that the possible arrhythmia is occurring usingthe third sensor. The controller sends the signal from the third sensorto the cardioverter so that the cardioverter may be able to determinewhether the possible arrhythmia is occurring.

Alternatively or additionally to any of the embodiments above, thesecond sensor may include an accelerometer, and the third sensor mayinclude a pressure sensor or an optical sensor.

Alternatively or additionally to any of the embodiments above, theverification request from the cardioverter may include an indication ofseverity of the possible arrhythmia, and if the indication of severityexceeds a threshold severity level, the controller may be configured toconcurrently activate the first sensor and the second sensor in order tomore quickly confirm or deny the possible arrhythmia.

Alternatively or additionally to any of the embodiments above, thecardioverter may be configured to examine a relationship between asignal from the first sensor and a signal from the second sensor toattempt to confirm that the possible arrhythmia is occurring.

Alternatively or additionally to any of the embodiments above, if thecontroller does not confirm that the possible arrhythmia is occurringusing the first sensor, the controller may be configured to activate thefirst sensor and the second sensor and to send a signal to thecardioverter so that the cardioverter can examine a relationship betweena signal from the first sensor and a signal from the second sensor toattempt to confirm that the possible arrhythmia is occurring.

In another example of the disclosure, a method of regulating a patient'sheart includes using a medical system including a cardioverter and aleadless cardiac pacemaker (LCP). The cardioverter may be configured tomonitor a cardiac EGM via electrodes disposed on an electrode supportand deliver shock therapy via the electrodes and the LCP may configuredto sense electrical cardiac activity via LCP electrodes disposed on theLCP and may include one or more additional sensors. The cardioverter maybe used in a chronic monitoring mode in which the cardioverter monitorsthe cardiac EGM for indications of a possible arrhythmia. An acute modemay be activated if the cardioverter identifies a possible arrhythmia,and the LCP may be instructed to help confirm the possible arrhythmiausing the LCP electrodes and/or at least one of the one or moreadditional sensors of the LCP. If the possible arrhythmia is confirmed(e.g. by the LCP or SICD), and if the possible arrhythmia is dangerous,shock therapy may be delivered to the heart via the electrodes of thecardioverter. If the possible arrhythmia is confirmed and is notdangerous, delivery of shock therapy to the heart via the electrodes ofthe cardioverter may be inhibited, and the acute mode continues in whichthe LCP electrodes and/or the at least one of the one or more additionalsensors of the LCP are used to monitor cardiac activity. If the possiblearrhythmia is not confirmed, delivery of shock therapy to the heart viathe electrodes of the cardioverter may be inhibited and the acute modemay continue in which the LCP electrodes and/or the at least one of theone or more additional sensors of the LCP are used to monitor cardiacactivity.

Alternatively or additionally to any of the embodiments above, thecardioverter may return to the chronic monitoring mode once the possiblearrhythmia has terminated.

Alternatively or additionally to any of the embodiments above, the oneor more additional sensors may include one or more of an accelerometer,a pressure sensor, and an optical sensor.

The above summary is not intended to describe each embodiment or everyimplementation of the present disclosure. Advantages and attainments,together with a more complete understanding of the disclosure, willbecome apparent and appreciated by referring to the followingdescription and claims taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing description of various illustrative embodiments in connectionwith the accompanying drawings, in which:

FIG. 1 is a highly schematic diagram of an illustrative system inaccordance with an example of the disclosure;

FIG. 2 is a graphical representation of an electrocardiogram (ECG)showing a temporal relationship between electrical signals of the heartand mechanical indications of contraction of the heart;

FIG. 3 is a graph showing example ECG signals, pressures, volumes andsounds within the heart over two example heart beats;

FIG. 4 is a schematic block diagram of an illustrative subcutaneousimplantable cardioverter defibrillator (SICD) usable in the system ofFIG. 1;

FIG. 5 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) useable in the system of FIG. 1;

FIG. 6 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) useable in the system of FIG. 1;

FIG. 7 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) useable in the system of FIG. 1;

FIG. 8 is a more detailed schematic block diagram of an illustrative LCPin accordance with an example of the disclosure;

FIG. 9 is a schematic block diagram of another illustrative medicaldevice that may be used in conjunction with the LCP of FIG. 8;

FIG. 10 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother;

FIG. 11 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with an example of the disclosure;

FIG. 12 is a side view of an illustrative implantable leadless cardiacdevice; and

FIG. 13 is a flow diagram of an illustrative method for regulating apatient's heart using the system of FIG. 1.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit aspects of thedisclosure to the particular illustrative embodiments described. On thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawingsin which similar elements in different drawings are numbered the same.The description and the drawings, which are not necessarily to scale,depict illustrative embodiments and are not intended to limit the scopeof the disclosure.

All numbers are herein assumed to be modified by the term “about”,unless the content clearly dictates otherwise. The recitation ofnumerical ranges by endpoints includes all numbers subsumed within thatrange (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include the plural referents unless thecontent clearly dictates otherwise. As used in this specification andthe appended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is contemplated that the feature,structure, or characteristic may be applied to other embodiments whetheror not explicitly described unless clearly stated to the contrary.

A normal, healthy heart induces contraction by conducting intrinsicallygenerated electrical signals throughout the heart. These intrinsicsignals cause the muscle cells or tissue of the heart to contract in acoordinated manner. These contractions forces blood out of and into theheart, providing circulation of the blood throughout the rest of thebody. Many patients suffer from cardiac conditions that affect theefficient operation of their hearts. For example, some hearts developdiseased tissue that no longer generate or efficiently conduct intrinsicelectrical signals. In some examples, diseased cardiac tissue mayconduct electrical signals at differing rates, thereby causing anunsynchronized and inefficient contraction of the heart. In otherexamples, a heart may generate intrinsic signals at such a low rate thatthe heart rate becomes dangerously low. In still other examples, a heartmay generate electrical signals at an unusually high rate, evenresulting in cardiac fibrillation. Implantable medical device are oftenused to treat such conditions by delivering one or more types ofelectrical stimulation therapy to the patient's heart.

FIG. 1 is a schematic diagram showing an illustrative system 10 that maybe used to sense and/or pace a heart H. In some cases, the system 10 mayalso be configured to be able to shock the heart H. The heart H includesa right atrium RA and a right ventricle RV. The heart H also includes aleft atrium LA and a left ventricle LV. In some cases, the system 10 mayinclude a medical device that provides anti-arrhythmic therapy to theheart H. In some cases, the medical device is an SICD (subcutaneousimplantable cardioverter defibrillator) 12. While not shown in thisFigure, in some cases the SICD 12 may include a lead that may beconfigured to be placed subcutaneously and outside of a patient'ssternum. In other cases, the lead may extend around or through thesternum and may be fixed adjacent an inner surface of the sternum. Inboth cases, the lead is positioned extracardially (outside of thepatient's heart). The SICD 12 may be configured to sense electricalactivity generated by the heart H as well as provide electrical energyto the heart H in order to shock the heart H from an undesired heartrhythm to a desired heart rhythm.

In some cases, the system 10 may include an intracardially implantedmedical device such as a cardiac monitor, a leadless cardiac pacemaker(LCP) or the like. In the example shown, the intracardially implantedmedical device is an LCP 14 that is configured to sense and/or pace theheart H. While a single LCP 14 is illustrated, it will be appreciatedthat two or more LCPs 14 may be implanted in or on the heart H. The LCP14 may be implanted into any chamber of the heart, such as the rightatrium RA, the left atrium LA, the right ventricle RV and the leftventricle LV. When more than one LCP is provided, each LCP may beimplanted in a different chamber. In some cases, multiple LCP's may beimplanted within a single chamber of the heart H.

In some cases, the SICD 12 and the LCP 14 may be implanted at the sametime. In some instances, depending on the cardiac deficiencies of aparticular patient, the SICD 12 may be implanted first, and one or moreLCPs 14 may be implanted at a later date if/when the patient developsindications for receiving cardiac resynchronization therapy and itbecomes necessary to pace the heart H. In some cases, it is contemplatedthat one or more LCPs 14 may be implanted first, in order to sense andpace the heart H. When a need for possible defibrillation becomesevident, the SICD 12 may subsequently be implanted. Regardless ofimplantation order or sequence, it will be appreciated that the SICD 12and the LCP 14 may communicate with each other using any desiredcommunications modality, such as conducted communication, inductivecommunication, acoustic communication, RF communication and/or using anyother suitable communication modality.

In situations in which the SICD 12 and the LCP 14 (or additional LCPs)are co-implanted, the SICD 12 may detect a possible arrhythmia. Ratherthan automatically delivering a defibrillation pulse, the SICD 12 maysend a verification request to a co-implanted LCP 14, requesting thatthe LCP 14, from its vantage point, verify whether the LCP 14 is alsodetecting the possible arrhythmia. In some cases, the LCP 14, uponreceiving the verification request, may activate one or more of aplurality of sensors to determine whether the LCP is able to confirm ordeny the possible arrhythmia seen by the SICD 12. In some cases,activating a sensor may include powering up a sensor that was previouslyunpowered. In some cases, activating a sensor may include increasing apower level of the sensor from a first lower power level to a secondhigher power level that may for example provide increased sensitivity.

In some cases, the LCP 14 may initially activate a first sensor. If thefirst sensor provides verification of the arrhythmia, the LCP 14 maycommunicate the verification to the SICD 12, which in response maydeliver a shock to cardiac tissue. If the first sensor is not able toprovide verification of the arrhythmia, or verify a lack of anarrhythmia, the LCP 14 may activate a second sensor that may, forexample, be more sensitive than the first sensor at the expense ofadditional power consumption. If the second sensor is able to provideverification of the arrhythmia, or verify a lack of an arrhythmia, theLCP 14 may communicate the verification to the SICD 12. If the secondsensor is not able to provide verification of the arrhythmia, or verifythe lack of an arrhythmia, the LCP 14 may activate a third sensor thatmay, for example, be more sensitive than the first sensor or the secondsensor at the expense of additional power consumption.

In some cases, the verification request from the SICD 12 may include anindication of severity of the possible arrhythmia. If, for example, thepossible arrhythmia is not severe, the LCP 14 may sequentially activateone sensor at a time, as described above, in order to verify or deny thepossible arrhythmia without consuming more power than needed. In somecases, however, if the possible arrhythmia is deemed severe, such as ifthe indication of severity exceeds a threshold severity level, the LCP14 may concurrently activate two or more sensors in order to morequickly provide either verification that the possible arrhythmia exists,or verification that the possible arrhythmia does not exist. If the LCP14 does not verify the possible arrhythmia initially detected by theSICD 12, the SICD 12 may delay or inhibit shock therapy.

In some cases, rather than sending a verification request upon initiallysensing a possible arrhythmia, the SICD 12 may instead instruct the LCP14 to activate a first sensor and then transmit a signal from the LCP 14providing the SICD 12 with the signal from the first sensor. If the SICD12 is not able to confirm the possible arrhythmia from the first sensordata, the SICD 12 may instruct the LCP 14 to activate a second sensorand then transmit a signal from the LCP 14 providing the SICD 12 withthe signal from the second sensor. If the SICD 12 is not able to confirmthe possible arrhythmia form the second sensor data, the SICD 12 mayinstruct the LCP 14 to activate a third sensor, or to activate severalsensors simultaneously. The SICD 12 may generate and deliver, or mayinhibit delivery of a shock to cardiac tissue based at least in partupon information received from the LCP 14.

In some cases, the LCP 14 may not be able to confirm the possiblearrhythmia, or the LCP 14 may not be able to communicate successfullywith the SICD 12 even if the LCP 14 is able to confirm the possiblearrhythmia. In some cases, for example, the SICD 12 may have a fail-safemode in which the SICD 12 will automatically react to a possiblearrhythmia if the LCP 14 is not able to confirm the possible arrhythmiaand/ or communicate its findings to the SICD 12. In some cases, this maybe a programmable setting. For some patients, a physician may programthe SICD 12 to default to inhibiting therapy if the LCP 14 is unable toconfirm. For other patients, a physician may program the SICD 12 todefault to delivering therapy if the LCP 14 is unable to confirm thepossible arrhythmia or communicate its findings. In some cases, the SICD12 may be programmed, if an immediately dangerous or fatal arrhythmia isdetected, to immediately deliver therapy without asking the LCP 14 forconfirmation and/or without waiting for a reply from the LCP 14. In somecases, how the SICD 12 responds to a possible arrhythmia, absentconfirmation from the LCP 14, may depend upon the severity of thepossible arrhythmia. For example, some arrhythmias such as atrialfibrillation, superventricular tachycardia and low rate (under 150 beatsper minutes) ventricular tachycardia may be considered as notimmediately dangerous. Other arrhythmias, such as ventricularfibrillation and high rate (over 220 beats per minute) ventriculartachycardia may be considered as being immediately dangerous, forexample.

With reference to FIG. 2, it will be appreciated that the heart H iscontrolled via electrical signals that pass through the cardiac tissueand that can be detected by implanted devices such as but not limited tothe SICD 12 and/or the LCP 14 of FIG. 1. FIG. 2 includes a portion of anelectrocardiogram (ECG) 16 along with a heart sounds trace 18. As can beseen in the ECG 16, a heartbeat includes a P-wave that indicates atrialdepolarization. A QRS complex, including a Q-wave, an R-wave and anS-wave, represents ventricular depolarization. A T-wave indicatesrepolarization of the ventricles. It will be appreciated that the ECG 16may be detected by implanted devices such as but not limited to the SICD12 and/or the LCP 14 of FIG. 1.

A number of heart sounds may also be detectable while the heart H beats.It will be appreciated that the heart sounds may be considered as onexample of mechanical indications of the heart beating. Otherillustrative mechanical indications may include, for example,endocardial acceleration or movement of a heart wall detected by anaccelerometer in the LCP, acceleration or movement of a heart walldetected by an accelerometer in the SICD, a pressure, pressure change,or pressure change rate in a chamber of the heart H detected by apressure sensor of the LCP, acoustic signals caused by heart movementsdetected by an acoustic sensor (e.g. accelerometer, microphone, etc.)and/or any other suitable indication of a heart chamber beating.

An electrical signal typically instructs a portion of the heart H tocontract, and then there is a corresponding mechanical response. In somecases, there may be a first heart sound that is denoted S1 and that isproduced by vibrations generated by closure of the mitral and tricuspidvalves during a ventricle contraction, a second heart sound that isdenoted S2 and that is produced by closure of the aortic and pulmonaryvalves, a third heart sound that is denoted S3 and that is an earlydiastolic sound caused by the rapid entry of blood from the right atriumRA into the right ventricle RV and from the left atrium LA into the leftventricle LV, and a fourth heart sound that is denoted S4 and that is alate diastolic sound corresponding to late ventricular filling during anactive atrial contraction.

Because the heart sounds are a result of cardiac muscle contracting orrelaxing in response to an electrical signal, it will be appreciatedthat there is a delay between the electrical signal, indicated by theECG 16, and the corresponding mechanical indication, indicated in theexample shown by the heart sounds trace 18. For example, the P-wave ofthe ECG 16 is an electrical signal triggering an atrial contraction. TheS4 heart sound is the mechanical signal caused by the atrialcontraction. In some cases, it may be possible to use this relationshipbetween the P-wave and the S4 heart sound. For example, if one of thesesignals may be detected, the relationship can be used as a timingmechanism to help search for the other. For example, if the P-wave canbe detected, a window following the P-wave can be defined and searchedin order to find and/or isolate the corresponding S4 heart sound. Insome cases, detection of both signals may be an indication of anincreased confidence level in a detected atrial contraction. In somecases, detection of either signal may be sufficient to identify anatrial contraction. The identity of an atrial contraction may be used toidentify an atrial contraction timing fiducial (e.g. a timing marker ofthe atrial contraction).

In some cases, the relationship of certain electrical signals and/ormechanical indications may be used to predict the timing of otherelectrical signals and/or mechanical indications within the sameheartbeat. Alternatively, or in addition, the timing of certainelectrical signals and/or mechanical indications corresponding to aparticular heartbeat may be used to predict the timing of otherelectrical signals and/or mechanical indications within a subsequentheartbeat. It will be appreciated that as the heart H undergoes acardiac cycle, the blood pressures and blood volumes within the heart Hwill vary over time. FIG. 3 illustrates how these parameters match upwith the electrical signals and corresponding mechanical indications.

FIG. 3 is a graph showing example pressures and volumes within a heartover time. More specifically, FIG. 3 shows an illustrative example ofthe aortic pressure, left ventricular pressure, left atrial pressure,left ventricular volume, an electrocardiogram (ECG), and heart sounds ofthe heart H over two consecutive heart beats. A cardiac cycle may beginwith diastole, and the mitral valve opens. The ventricular pressurefalls below the atrial pressure, resulting in the ventricular fillingwith blood. During ventricular filling, the aortic pressure slowlydecreases as shown. During systole, the ventricle contracts. Whenventricular pressure exceeds the atrial pressure, the mitral valvecloses, generating the S1 heart sound. Before the aortic valve opens, anisovolumetric contraction phase occurs where the ventricle pressurerapidly increases but the ventricle volume does not significantlychange. Once the ventricular pressure equals the aortic pressure, theaortic valve opens and the ejection phase begins where blood is ejectedfrom the left ventricle into the aorta. The ejection phase continuesuntil the ventricular pressure falls below the aortic pressure, at whichpoint the aortic valve closes, generating the S2 heart sound. At thispoint, the isovolumetric relaxation phase begins and ventricularpressure falls rapidly until it is exceeded by the atrial pressure, atwhich point the mitral valve opens and the cycle repeats. Cardiacpressure curves for the pulmonary artery, the right atrium, and theright ventricle, and the cardiac volume curve for the right ventricle,may be similar to those illustrated in FIG. 3. In many cases, thecardiac pressure in the right ventricle is lower than the cardiacpressure in the left ventricle.

FIG. 4 is a schematic illustration of a subcutaneous implantablecardioverter defibrillator (SICD) 20 that may, for example, beconsidered as being a representative example of the SICD 12 shown inFIG. 1. In some cases, the SICD 20 includes a housing 22 and anelectrode support 24 that is operably coupled to the housing 22. In somecases, the electrode support 24 may be configured to place one or moreelectrodes in a position, such as subcutaneous or sub-sternal, thatenables the one or more electrodes to detect cardiac electrical activityas well as to be able to deliver electrical shocks when appropriate tothe heart. In the example shown, the housing 22 includes a controller26, a power supply 28 and a communications module 30. As illustrated,the electrode support 24 includes a first electrode 32, a secondelectrode 34 and a third electrode 36. In some cases, the electrodesupport 24 may include fewer or more electrodes. In some cases, theelectrode support 24 may include one or more other sensors such as anaccelerometer or a gyro, for example.

It will be appreciated that the SICD 20 may include additionalcomponents which are not illustrated here for simplicity. The powersupply 28 is operably coupled to the controller 26 and provides thecontroller 26 with power to operate the controller 26, to sendelectrical power to the electrodes on or in the electrode support 24,and to send signals to the communications module 30, as appropriate.

In some cases, the controller 26 may be configured to sense a possiblearrhythmia via the electrodes on or in the electrode support 24, and maysend a verification request to an LCP such as the LCP 14 (FIG. 1) viathe communications module 30. The controller 26 may subsequently receivea signal from the LCP 14, via the communications module 30, that informsthe controller 26 as to whether the possible arrhythmia has beenconfirmed (or not confirmed). In some cases, the controller 26 maysubsequently receive a signal from the LCP 14, via the communicationsmodule 30, that confirms the existence of the possible arrhythmia andidentifies the type of arrhythmia (e.g. Ventricular Tachycardia,Ventricular Fibrillation, Premature Ventricular Contractions,supraventricular Arrhythmias such as Supraventricular Tachycardia (SVT)or Paroxysmal Supraventricular Tachycardia (PSVT), atrial fibrillation).

FIG. 5 is a schematic illustration of a leadless cardiac pacemaker (LCP)40 that may, for example, be considered as representing the LCP 14 shownin FIG. 1. In some cases, the LCP 40 includes a housing 42. Asillustrated, a first electrode 44 and a second electrode 47 are eachdisposed relative to the housing 42 and may, for example, be exposed toan environment exterior to the housing 42 when the LCP 40 is implantedin the heart. In some cases, the LCP 40 includes a controller 46, apower supply 48 and a communications module 50. The power supply 48 maybe operably coupled to the controller 46 and provides the controller 46with power to operate the controller 46, to send communication signalssuch as but not limited to conducted communications through the firstelectrode 44 and the second electrode 47 via the communications module50 as well as providing pacing pulses via the first electrode 44 and thesecond electrode 47. While two electrodes 44, 47 are illustrated, itwill be appreciated that in some cases the LCP 40 may include additionalelectrodes (not shown), and that different electrodes or vectors may beused for sensing and/or pacing, if desired.

In some cases, the communications module 50 may be configured to receivea verification request signal from the SICD 12 when the SICD 12 detectsa possible arrhythmia. In some cases, the verification request includesa type of arrhythmia. The communications module 50 may be configured tosubsequently send a signal to the SICD 12 that the possible arrhythmiahas been confirmed. In some cases, the communications module 50 may senda signal to the SICD 12 that not only confirms the existence of thepossible arrhythmia but also confirms the type of arrhythmia or notifiesthe SICD 12 of the type of arrhythmia. In some cases, the communicationsmodule 50 may be configured to send a signal to the SICD 12 thatconfirmed the absence of the possible arrhythmia. In some cases, thecommunications module 50 may be configured to send a signal to the SICD12 that indicates neither the existence nor the absence of the possiblearrhythmia could be confirmed.

The illustrative LCP 40 includes a plurality of sensors 52 that areoperably coupled to the controller 46. As illustrated, the plurality ofsensors 52 includes a sensor 52 a, a sensor 52 b, a sensor 52 c and asensor 52 d. In some cases, the plurality of sensors 52 may includefewer sensors. In some instances, the plurality of sensors 52 mayinclude additional sensors not shown. In some cases, it will beappreciated that the first electrode 44 and the second electrode 47 may,in combination, function as a sensor by sensing, for example, intrinsicand/or evoked cardiac electrical signals. It will be appreciated thatone or more of the plurality of sensors 52 may, for example, include asensor that is configured to detect heart sounds, pressure, cardiac wallmovement, chamber volume, stroke volume, or other parameters. One ormore of the plurality of sensors 52 may be an accelerometer, a pressuresensor, a gyro, and/or an optical sensor, for example.

In some cases, when the LCP 40 receives a verification request from theSICD 12 to verify the existence of a possible arrhythmia detected by theSICD 12, the controller 46 may be configured to activate one or more ofthe plurality of sensors 52 from a lower power state to a higher powerstate, and to use the activated one or more of the plurality of sensors52 to attempt to confirm that the possible arrhythmia is occurring. Ifthe LCP 40 is able to confirm the possible arrhythmia using theactivated one or more of the plurality of sensors 52, the LCP 40 may beconfigured to send a confirmation response to the SICD 12 confirming thearrhythmia. It will be appreciated that in response to receiving theconfirmation response, the SICD 12 may be configured to generate anddeliver a shock to cardiac tissue if appropriate. In some cases, theSICD 12 may delay or otherwise inhibit delivery of a shock to cardiactissue, particularly if the LCP 40 does not confirm the arrhythmia.

In some cases, the plurality of sensors 52 may include a first sensorsuch as sensor 52 a that when activated consumes a first level of powerand a second sensor such as sensor 52 b that when activated consumes asecond level of power that is higher than the first level of power. Insome cases, the second sensor 52 b may provide an increased level ofaccuracy or sensitivity relative to that provided by the first sensor 52a, and/or may sense a different parameter that might be better suited todetect the particular arrhythmia. In some cases, upon receiving averification request from the SICD 12, the LCP 40 may initially activatethe first sensor 52 a in order to try to confirm or deny the possiblearrhythmia. If the LCP 40 is able to do so using the first sensor 52 a,the LCP 40 may be configured to send a confirmation signal to the SICD12. However, if the LCP 40 is not able to confirm or deny the possiblearrhythmia using the first sensor 52 a, the LCP 40 may be configured toactivate the second sensor 52 b in order to attempt to confirm or denythe possible arrhythmia. If the LCP 40 is able to confirm or deny thepossible arrhythmia using the second sensor 52 b, the LCP 40 may send aconfirmation response to the SICD 12.

In some cases, the plurality of sensors 52 may include a third sensorsuch as sensor 52 c that when activated, consumes a third level of powerthat is higher than that consumed by the second sensor 52 b whenactivated. In some cases, the third sensor 52 c may provide an increasedaccuracy or sensitivity, and/or may sense a different parameter thatmight be better suited to detect the particular arrhythmia, thatjustifies the increased power consumption. If the LCP 40 was not able toconfirm or deny the possible arrhythmia using the first sensor 52 a orthe second sensor 52 b, the LCP 40 may be configured to activate thethird sensor 52 c in order to attempt to confirm or deny the possiblearrhythmia. If the LCP 40 is able to confirm or deny the possiblearrhythmia using the third sensor 52 c, the LCP 40 may be configured tosend a confirmation response to the SICD 12.

In some cases, the first sensor 52 a represents the LCP 40 detectingelectrical cardiac activity via the first electrode 44 and the secondelectrode 47, or using one of the first electrode 44 and the secondelectrode 47 in combination with a third or fourth electrode (notillustrated). In some cases, the second sensor 52 b may be configured todetect heart sounds. In some cases, the second sensor 52 b may, forexample, be an accelerometer that is disposed relative to the LCP 40. Insome cases, the second sensor 52 b may be a pressure sensor that isdisposed relative to the LCP 40. In some cases, the third sensor 52 cmay be an optical sensor. These are just examples. By activating thesensors in sequence, often starting with the sensor with the lowestpower consumption, power savings may be realized.

In some cases, the LCP 40 may concurrently activate two or more of theplurality of sensors 52. In some cases, the LCP 40 may be configured toexamine a relationship between a signal from the first of the two ormore sensors and a signal from the second of the two or more sensors toattempt to confirm or deny the possible arrhythmia detected by the SICD12. For example, in some cases, a signal representing an S2 heart soundmay be compared with a signal representing a pressure waveform in orderto confirm hemodynamic stability. If the patient is hemodynamicallystable, the S2 heart sound should be detected shortly after theventricular pressure peaks, for example. If the timing is not asexpected, this may provide verification of the possible arrhythmia seenby the SICD 12.

In some cases, and as referenced above, the verification request thatthe LCP 40 receives from the SICD 12 may include an indication ofseverity of the possible arrhythmia. For example, if the possiblearrhythmia is deemed not to be immediately dangerous to the health ofthe patient, the LCP 40 may sequentially activate the plurality ofsensors 52 one at a time, as needed, in trying to confirm or deny thepossible arrhythmia. In some cases, however, if the possible arrhythmiais deemed to be possibly immediately dangerous to the health of thepatient, and thus the indication of severity exceeds a thresholdseverity level, the LCP 40 may be configured to concurrently activatetwo or more of the plurality of sensors 52 in order to more quicklyconfirm or deny the possible arrhythmia. In some cases, the thresholdseverity level may be programmed into the LCP 40 upon manufacture. Insome instances, the threshold severity level may be customized for aparticular patient, and in some cases may vary over time, by posture, byactivity level, and/or any other suitable condition.

In some cases, there may be several LCPs 40 that are co-implanted (suchas but not limited to the LCP 302 and the LCP 304 shown in FIG. 10). Insome cases, the two LCPs may cooperate to provide sensor functionality.For example, a first LCP may inject current into the heart using two ormore of its electrodes. The second LCP may measure a resulting voltageacross two or more of its electrodes. This may provide an impedancemeasurement of the tissue surrounding the first LCP and the second LCP.As another example, a first LCP may inject an ultrasonic pulse into theheart using an ultrasonic transmitting antenna. A second LCP may measurethe ultrasonic energy using an ultrasonic receiving antenna, therebyproviding a distance and/or density measurement of the tissue betweenthe first LCP and the second LCP.

FIG. 6 is a schematic illustration of a leadless cardiac pacemaker (LCP)60 that may, for example, be considered as representing the LCP 14 shownin FIG. 1. In some cases, the LCP 60 includes a housing 62. Asillustrated, a first electrode 64 and a second electrode 66 are eachdisposed relative to the housing 62 and may, for example, be exposed toan environment exterior to the housing 62 when the LCP 60 is implantedin the heart. In some cases, the LCP 60 includes a controller 68, apower supply 70 and a communications module 72. The power supply 70 maybe operably coupled to the controller 68 and provides the controller 68with power to operate the controller 68, to send communication signalssuch as but not limited to conducted communications through the firstelectrode 64 and the second electrode 66 via the communications module72 as well as providing pacing pulses via the first electrode 64 and thesecond electrode 66. While two electrodes 64, 66 are illustrated, itwill be appreciated that in some cases the LCP 60 may include additionalelectrodes (not shown).

In some cases, the communications module 72 may be configured to receivea verification request signal from the SICD 12 when the SICD 12 detectsa possible arrhythmia. The communications module 72 may be configured tosubsequently send a signal to the SICD 12 that the possible arrhythmiahas been confirmed, or that an absence of an arrhythmia is confirmed. Insome cases, the LCP 60 includes a first sensor 74 and a second sensor76. In some cases, the first sensor 74, when activated, consumes a firstlevel of power. In some cases, the second sensor 76, when activated,consumes a second level of power that is higher than the first level ofpower. In some cases, and to justify the relatively higher powerconsumption, the second sensor 76 may provide an increased level ofaccuracy or sensitivity relative that that of the first sensor 74, or isconfigured to detect a different parameter that might be better suitedto detect the particular arrhythmia.

In some cases, upon receiving a verification request from the SICD 12via the communications module 72, the controller 68 may be configured toinitially sense cardiac activity using the first sensor 74 to attempt toconfirm that the possible arrhythmia is occurring while the secondsensor 76 is in a lower power state. The lower power state may be in anoff state that draws no power, or a sleep or other lower power statethat draws some power. If the controller 68 is able to confirm that thepossible arrhythmia is occurring using the first sensor 74, thecontroller 68 may be configured to send a confirmation response to theSICD 12 via the communications module 72 confirming that the possiblearrhythmia is occurring.

However, if the controller 68 is not able to confirm that the possiblearrhythmia is occurring using the first sensor 74, the controller 68 maybe configured to activate the second sensor 76 from the lower powerstate to a higher power state, and then attempt to confirm that thepossible arrhythmia is occurring using the second sensor 76 (e.g. usingjust the second sensor 76 or using the first sensor 74 and the secondsensor 76). If the controller 68 is able to confirm that the possiblearrhythmia is occurring using the second sensor 76, the controller 68may be configured to send the confirmation response to the SICD 12 viathe communications module 72 confirming that the possible arrhythmia isoccurring. If the controller 68 is not able to confirm the possiblearrhythmia using only the first sensor 74, the controller 68 may beconfigured to activate both the first sensor 74 and the second sensor 76at the same time, as noted above, and then examine a relationshipbetween a signal from the first sensor 74 and a signal from the secondsensor 76 to attempt to confirm the possible arrhythmia. In some cases,the second sensor 76 may be an accelerometer or a pressure sensor.

FIG. 7 is a schematic illustration of a leadless cardiac pacemaker (LCP)80 that may, for example, be considered as representing the LCP 14 shownin FIG. 1. In some cases, the LCP 80 includes a housing 82. Asillustrated, a first electrode 84 and a second electrode 86 are eachdisposed relative to the housing 82 and may, for example, be exposed toan environment exterior to the housing 82 when the LCP 80 is implantedin the heart. In some cases, the LCP 80 includes a controller 88, apower supply 90 and a communications module 92. The power supply 90 maybe operably coupled to the controller 88 and provides the controller 88with power to operate the controller 88, to send communication signalssuch as but not limited to conducted communications through the firstelectrode 84 and the second electrode 86 via the communications module92 as well as providing pacing pulses via the first electrode 84 and thesecond electrode 86. While two electrodes 84, 86 are illustrated, itwill be appreciated that in some cases the LCP 80 may include additionalelectrodes (not shown).

In some cases, the communications module 72 may be configured to receivea verification request signal from the SICD 12 when the SICD 12 detectsa possible arrhythmia. The communications module 92 may be configured tosubsequently send a signal to the SICD 12 that the possible arrhythmiahas been confirmed, or that an absence of an arrhythmia is confirmed, orneither. In some cases, the first electrode 84 and the second electrode86 may, in combination, form a first sensor that is able to sensecardiac electrical activity. In some cases, the LCP 80 includes a secondsensor 94. Optionally, the LCP 80 may include a third sensor 96. Asdiscussed with respect to the LCP 40 (FIG. 5) and the LCP 60 (FIG. 6),the controller 88 may be configured to sequentially or simultaneously,as desired, activate the first sensor, the second sensor 94 and thethird sensor 96 to attempt to confirm or deny a possible arrhythmia.

To confirm the possible arrhythmia, the LCP 80 and/or SICD 12 may use aLCP electrogram (EGM)signal detected by electrodes 84/86 of the LCP 80and/or an SICD EGM detected by electrodes of the SICD 12 to help confirmor deny a detected possible arrhythmia. For example, the LCP 80 and/orSICD 12 may use the LCP EGM signal to confirm the heart rate sensed bythe SICD 12 by detecting T-waves that are sensed by the SICD 12 asR-waves. In another example, the LCP 80 and/or SICD 12 may use R-wave toR-wave variability between beats to confirm or deny if an unstablerhythm is present. The R-waves may be detected by the LCP 80. The LCP 80and/or SICD 12 may use the P-wave to R-wave interval to helpdifferentiate between SVT from VT/VF. If the PR interval (e.g. P fromthe SICD EGM and R from the LCP EGM) is not stable, then the arrhythmiamay be considered VF, and the SICD may proceed to delivery shocktherapy. If the PR interval is stable, then the arrhythmia may be apossible sinus VT, in which case the LCP 80 may activate anaccelerometer to detect if S1/S2 is low and/or if the LV pressure islow. If either is low, the arrhythmia may be considered VF, and the SICDmay proceed to delivery shock therapy. If neither is low, the SICD maydelay or inhibit shock therapy. In another example, the LCP 80 and/orSICD 12 may use the association between the QRS complex and the S1 heartsound, as detected by the LCP 80, to confirm the heart rate. A measureof reliability of each sensor reading or combination of sensor readingsmay be used to determine a confidence level score in whether thepossible arrhythmia is actually present.

In some cases, the LCP 80 and/or SICD 12 may use heart sounds detectedby the LCP 80 (e.g. via second sensor 94, such as an accelerometer) tohelp confirm or deny a possible arrhythmia. For example, the LCP 80and/or SICD 12 may use the S1/S2 amplitude to detect a measure ofhemodynamic stability. In some cases, the LCP 80 and/or SICD 12 may useS1/S2 timing to confirm heart rate. The LCP 80 and/or SICD 12 may useS1/S2 variability to confirm or deny an unstable rhythm. The LCP 80and/or SICD 12 may use R-wave to S1, R-wave to S2, and/or S2 to R-wavevariability to help differentiate between sinus VT from VF.

It is contemplated that the LCP 80 and/or SICD 12 may use pressuredetected by the LCP 80 (e.g. via third sensor 96, such as a pressuresensor) to help confirm or deny a possible arrhythmia. For example, theLCP 80 and/or SICD 12 may use variations of pressure in the heart toprovide a measure of hemodynamic stability of the heart (e.g. standarddeviation of max or min pressures, dp/dt and/or other pressureparameters over several beats, variation of max or min pressures, dp/dtor other pressure parameters over several beats, etc.). In some cases,the LCP 80 and/or SICD 12 may use the absolute value of the pressure toprovide a measure of hemodynamic stability and/or perfusion status ofthe heart (e.g. End Systolic Pressure (ESP), End Diastolic Pressure(EDP), mean pressure, peak pressure). The LCP 80 and/or SICD 12 may usean association between the pressure wave and S2 to confirm the heartrate and/or to confirm proper S2 detection.

The LCP 80 and/or SICD 12 may use other parameters detected by the LCP80 to help confirm or deny a possible arrhythmia. For example, the LCPmay monitor an impedance between the LCP electrodes 84 and 86 todetermine a measure of the volume of the chamber, and in some cases, ameasure of stroke volume fluctuations. Alternatively, or in addition,the LCP may include one or more optical sensor to obtain a measure thevolume of the chamber. These are just examples sensor measurements thatmay be used.

FIG. 8 depicts another illustrative leadless cardiac pacemaker (LCP)that may be implanted into a patient and may operate to deliverappropriate therapy to the heart, such as to deliver anti-tachycardiapacing (ATP) therapy, cardiac resynchronization therapy (CRT),bradycardia therapy, and/or the like. As can be seen in FIG. 8, the LCP100 may be a compact device with all components housed within the ordirectly on a housing 120. In some cases, the LCP 100 may be consideredas being an example of one or more of the LCP 14 (FIG. 1), the LCP 40(FIG. 5) and/or the LCP 60 (FIG. 6). In the example shown in FIG. 8, theLCP 100 may include a communication module 102, a pulse generator module104, an electrical sensing module 106, a mechanical sensing module 108,a processing module 110, a battery 112, and an electrode arrangement114. The LCP 100 may include more or less modules, depending on theapplication.

The communication module 102 may be configured to communicate withdevices such as sensors, other medical devices such as an SICD, and/orthe like, that are located externally to the LCP 100. Such devices maybe located either external or internal to the patient's body.Irrespective of the location, external devices (i.e. external to the LCP100 but not necessarily external to the patient's body) can communicatewith the LCP 100 via communication module 102 to accomplish one or moredesired functions. For example, the LCP 100 may communicate information,such as sensed electrical signals, data, instructions, messages, R-wavedetection markers, etc., to an external medical device (e.g. SICD and/orprogrammer) through the communication module 102. The external medicaldevice may use the communicated signals, data, instructions, messages,R-wave detection markers, etc., to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, and/or performing any othersuitable function. The LCP 100 may additionally receive information suchas signals, data, instructions and/or messages from the external medicaldevice through the communication module 102, and the LCP 100 may use thereceived signals, data, instructions and/or messages to perform variousfunctions, such as determining occurrences of arrhythmias, deliveringelectrical stimulation therapy, storing received data, and/or performingany other suitable function. The communication module 102 may beconfigured to use one or more methods for communicating with externaldevices. For example, the communication module 102 may communicate viaradiofrequency (RF) signals, inductive coupling, optical signals,acoustic signals, conducted communication signals, and/or any othersignals suitable for communication.

In the example shown in FIG. 8, the pulse generator module 104 may beelectrically connected to the electrodes 114. In some examples, the LCP100 may additionally include electrodes 114′. In such examples, thepulse generator 104 may also be electrically connected to the electrodes114′. The pulse generator module 104 may be configured to generateelectrical stimulation signals. For example, the pulse generator module104 may generate and deliver electrical stimulation signals by usingenergy stored in the battery 112 within the LCP 100 and deliver thegenerated electrical stimulation signals via the electrodes 114 and/or114′. Alternatively, or additionally, the pulse generator 104 mayinclude one or more capacitors, and the pulse generator 104 may chargethe one or more capacitors by drawing energy from the battery 112. Thepulse generator 104 may then use the energy of the one or morecapacitors to deliver the generated electrical stimulation signals viathe electrodes 114 and/or 114′. In at least some examples, the pulsegenerator 104 of the LCP 100 may include switching circuitry toselectively connect one or more of the electrodes 114 and/or 114′ to thepulse generator 104 in order to select which of the electrodes 114/114′(and/or other electrodes) the pulse generator 104 delivers theelectrical stimulation therapy. The pulse generator module 104 maygenerate and deliver electrical stimulation signals with particularfeatures or in particular sequences in order to provide one or multipleof a number of different stimulation therapies. For example, the pulsegenerator module 104 may be configured to generate electricalstimulation signals to provide electrical stimulation therapy to combatbradycardia, tachycardia, cardiac synchronization, bradycardiaarrhythmias, tachycardia arrhythmias, fibrillation arrhythmias, cardiacsynchronization arrhythmias and/or to produce any other suitableelectrical stimulation therapy. Some more common electrical stimulationtherapies include anti-tachycardia pacing (ATP) therapy, cardiacresynchronization therapy (CRT), and cardioversion/defibrillationtherapy.

In some examples, the LCP 100 may not include a pulse generator 104. Forexample, the LCP 100 may be a diagnostic only device. In such examples,the LCP 100 may not deliver electrical stimulation therapy to a patient.Rather, the LCP 100 may collect data about cardiac electrical activityand/or physiological parameters of the patient and communicate such dataand/or determinations to one or more other medical devices via thecommunication module 102.

In some examples, the LCP 100 may include an electrical sensing module106, and in some cases, a mechanical sensing module 108. The electricalsensing module 106 may be configured to sense the cardiac electricalactivity of the heart. For example, the electrical sensing module 106may be connected to the electrodes 114/114′, and the electrical sensingmodule 106 may be configured to receive cardiac electrical signalsconducted through the electrodes 114/114′. The cardiac electricalsignals may represent local information from the chamber in which theLCP 100 is implanted. For instance, if the LCP 100 is implanted within aventricle of the heart (e.g. RV, LV), cardiac electrical signals sensedby the LCP 100 through the electrodes 114/114′ may represent ventricularcardiac electrical signals. In some cases, the LCP 100 may be configuredto detect cardiac electrical signals from other chambers (e.g. farfield), such as the P-wave from the atrium.

The mechanical sensing module 108 may include one or more sensors, suchas an accelerometer, a pressure sensor, a heart sound sensor, ablood-oxygen sensor, a chemical sensor, a temperature sensor, a flowsensor and/or any other suitable sensors that are configured to measureone or more mechanical/chemical parameters of the patient. Both theelectrical sensing module 106 and the mechanical sensing module 108 maybe connected to a processing module 110, which may provide signalsrepresentative of the sensed mechanical parameters. Although describedwith respect to FIG. 8 as separate sensing modules, in some cases, theelectrical sensing module 206 and the mechanical sensing module 208 maybe combined into a single sensing module, as desired.

The electrodes 114/114′ can be secured relative to the housing 120 butexposed to the tissue and/or blood surrounding the LCP 100. In somecases, the electrodes 114 may be generally disposed on either end of theLCP 100 and may be in electrical communication with one or more of themodules 102, 104, 106, 108, and 110. The electrodes 114/114′ may besupported by the housing 120, although in some examples, the electrodes114/114′ may be connected to the housing 120 through short connectingwires such that the electrodes 114/114′ are not directly securedrelative to the housing 120. In examples where the LCP 100 includes oneor more electrodes 114′, the electrodes 114′ may in some cases bedisposed on the sides of the LCP 100, which may increase the number ofelectrodes by which the LCP 100 may sense cardiac electrical activity,deliver electrical stimulation and/or communicate with an externalmedical device. The electrodes 114/114′ can be made up of one or morebiocompatible conductive materials such as various metals or alloys thatare known to be safe for implantation within a human body. In someinstances, the electrodes 114/114′ connected to the LCP 100 may have aninsulative portion that electrically isolates the electrodes 114/114′from adjacent electrodes, the housing 120, and/or other parts of the LCP100. In some cases, one or more of the electrodes 114/114′ may beprovided on a tail (not shown) that extends away from the housing 120.

The processing module 110 can be configured to control the operation ofthe LCP 100. For example, the processing module 110 may be configured toreceive electrical signals from the electrical sensing module 106 and/orthe mechanical sensing module 108. Based on the received signals, theprocessing module 110 may determine, for example, abnormalities in theoperation of the heart H. Based on any determined abnormalities, theprocessing module 110 may control the pulse generator module 104 togenerate and deliver electrical stimulation in accordance with one ormore therapies to treat the determined abnormalities. The processingmodule 110 may further receive information from the communication module102. In some examples, the processing module 110 may use such receivedinformation to help determine whether an abnormality is occurring,determine a type of abnormality, and/or to take particular action inresponse to the information. The processing module 110 may additionallycontrol the communication module 102 to send/receive information to/fromother devices.

In some examples, the processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip and/or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of the LCP 100. By using a pre-programmed chip, the processingmodule 110 may use less power than other programmable circuits (e.g.general purpose programmable microprocessors) while still being able tomaintain basic functionality, thereby potentially increasing the batterylife of the LCP 100. In other examples, the processing module 110 mayinclude a programmable microprocessor. Such a programmablemicroprocessor may allow a user to modify the control logic of the LCP100 even after implantation, thereby allowing for greater flexibility ofthe LCP 100 than when using a pre-programmed ASIC. In some examples, theprocessing module 110 may further include a memory, and the processingmodule 110 may store information on and read information from thememory. In other examples, the LCP 100 may include a separate memory(not shown) that is in communication with the processing module 110,such that the processing module 110 may read and write information toand from the separate memory.

The battery 112 may provide power to the LCP 100 for its operations. Insome examples, the battery 112 may be a non-rechargeable lithium-basedbattery. In other examples, a non-rechargeable battery may be made fromother suitable materials, as desired. Because the LCP 100 is animplantable device, access to the LCP 100 may be limited afterimplantation. Accordingly, it is desirable to have sufficient batterycapacity to deliver therapy over a period of treatment such as days,weeks, months, years or even decades. In some instances, the battery 112may a rechargeable battery, which may help increase the useable lifespanof the LCP 100. In still other examples, the battery 112 may be someother type of power source, as desired.

To implant the LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix the LCP 100 to the cardiac tissueof the patient's heart. To facilitate fixation, the LCP 100 may includeone or more anchors 116. The anchor 116 may include any one of a numberof fixation or anchoring mechanisms. For example, the anchor 116 mayinclude one or more pins, staples, threads, screws, helix, tines, and/orthe like. In some examples, although not shown, the anchor 116 mayinclude threads on its external surface that may run along at least apartial length of the anchor 116. The threads may provide frictionbetween the cardiac tissue and the anchor to help fix the anchor 116within the cardiac tissue. In other examples, the anchor 116 may includeother structures such as barbs, spikes, or the like to facilitateengagement with the surrounding cardiac tissue.

FIG. 9 depicts an example of another medical device (MD) 200, which maybe used in conjunction with the LCP 100 (FIG. 8) in order to detectand/or treat cardiac abnormalities. In some cases, the MD 200 may beconsidered as an example of the SICD 12 (FIG. 1). In the example shown,the MD 200 may include a communication module 202, a pulse generatormodule 204, an electrical sensing module 206, a mechanical sensingmodule 208, a processing module 210, and a battery 218. Each of thesemodules may be similar to the modules 102, 104, 106, 108, and 110 of LCP100. Additionally, the battery 218 may be similar to the battery 112 ofthe LCP 100. In some examples, however, the MD 200 may have a largervolume within the housing 220. In such examples, the MD 200 may includea larger battery and/or a larger processing module 210 capable ofhandling more complex operations than the processing module 110 of theLCP 100.

While it is contemplated that the MD 200 may be another leadless devicesuch as shown in FIG. 8, in some instances the MD 200 may include leadssuch as leads 212. The leads 212 may include electrical wires thatconduct electrical signals between the electrodes 214 and one or moremodules located within the housing 220. In some cases, the leads 212 maybe connected to and extend away from the housing 220 of the MD 200. Insome examples, the leads 212 are implanted on, within, or adjacent to aheart of a patient. The leads 212 may contain one or more electrodes 214positioned at various locations on the leads 212, and in some cases atvarious distances from the housing 220. Some leads 212 may only includea single electrode 214, while other leads 212 may include multipleelectrodes 214. Generally, the electrodes 214 are positioned on theleads 212 such that when the leads 212 are implanted within the patient,one or more of the electrodes 214 are positioned to perform a desiredfunction. In some cases, the one or more of the electrodes 214 may be incontact with the patient's cardiac tissue. In some cases, the one ormore of the electrodes 214 may be positioned subcutaneously and outsideof the patient's heart. In some cases, the electrodes 214 may conductintrinsically generated electrical signals to the leads 212, e.g.signals representative of intrinsic cardiac electrical activity. Theleads 212 may, in turn, conduct the received electrical signals to oneor more of the modules 202, 204, 206, and 208 of the MD 200. In somecases, the MD 200 may generate electrical stimulation signals, and theleads 212 may conduct the generated electrical stimulation signals tothe electrodes 214. The electrodes 214 may then conduct the electricalsignals and delivery the signals to the patient's heart (either directlyor indirectly).

The mechanical sensing module 208, as with the mechanical sensing module108, may contain or be electrically connected to one or more sensors,such as accelerometers, acoustic sensors, blood pressure sensors, heartsound sensors, blood-oxygen sensors, and/or other sensors which areconfigured to measure one or more mechanical/chemical parameters of theheart and/or patient. In some examples, one or more of the sensors maybe located on the leads 212, but this is not required. In some examples,one or more of the sensors may be located in the housing 220.

While not required, in some examples, the MD 200 may be an implantablemedical device. In such examples, the housing 220 of the MD 200 may beimplanted in, for example, a transthoracic region of the patient. Thehousing 220 may generally include any of a number of known materialsthat are safe for implantation in a human body and may, when implanted,hermetically seal the various components of the MD 200 from fluids andtissues of the patient's body.

In some cases, the MD 200 may be an implantable cardiac pacemaker (ICP).In this example, the MD 200 may have one or more leads, for example theleads 212, which are implanted on or within the patient's heart. The oneor more leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. The MD200 may be configured to sense intrinsically generated cardiacelectrical signals and determine, for example, one or more cardiacarrhythmias based on analysis of the sensed signals. The MD 200 may beconfigured to deliver CRT, ATP therapy, bradycardia therapy, and/orother therapy types via the leads 212 implanted within the heart. Insome examples, the MD 200 may additionally be configured providedefibrillation therapy.

In some instances, the MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, the MD 200 mayinclude one or more leads implanted within a patient's heart. The MD 200may also be configured to sense cardiac electrical signals, determineoccurrences of tachyarrhythmias based on the sensed signals, and may beconfigured to deliver defibrillation therapy in response to determiningan occurrence of a tachyarrhythmia. In other examples, the MD 200 may bea subcutaneous implantable cardioverter-defibrillator (S-ICD). Inexamples where the MD 200 is an S-ICD, one of the leads 212 may be asubcutaneously implanted lead. In at least some examples where the MD200 is an S-ICD, the MD 200 may include only a single lead which isimplanted subcutaneously, but this is not required. In some instances,the lead(s) may have one or more electrodes that are placedsubcutaneously and outside of the chest cavity. In other examples, thelead(s) may have one or more electrodes that are placed inside of thechest cavity, such as just interior of the sternum.

In some examples, the MD 200 may not be an implantable medical device.Rather, the MD 200 may be a device external to the patient's body, andmay include skin-electrodes that are placed on a patient's body. In suchexamples, the MD 200 may be able to sense surface electrical signals(e.g. cardiac electrical signals that are generated by the heart orelectrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin). In such examples, theMD 200 may be configured to deliver various types of electricalstimulation therapy, including, for example, defibrillation therapy.

FIG. 10 illustrates an example of a medical device system and acommunication pathway through which multiple medical devices 302, 304,306, and/or 310 may communicate. In the example shown, the medicaldevice system 300 may include LCPs 302 and 304, external medical device306, and other sensors/devices 310. The external device 306 may be anyof the devices described previously with respect to the MD 200. Othersensors/devices 310 may also be any of the devices described previouslywith respect to the MD 200. In some instances, other sensors/devices 310may include a sensor, such as an accelerometer, an acoustic sensor, ablood pressure sensor, or the like. In some cases, other sensors/devices310 may include an external programmer device that may be used toprogram one or more devices of the system 300.

Various devices of the system 300 may communicate via communicationpathway 308. For example, the LCPs 302 and/or 304 may sense intrinsiccardiac electrical signals and may communicate such signals to one ormore other devices 302/304, 306, and 310 of the system 300 viacommunication pathway 308. In one example, one or more of the devices302/304 may receive such signals and, based on the received signals,determine an occurrence of an arrhythmia. In some cases, the device ordevices 302/304 may communicate such determinations to one or more otherdevices 306 and 310 of the system 300. In some cases, one or more of thedevices 302/304, 306, and 310 of the system 300 may take action based onthe communicated determination of an arrhythmia, such as by delivering asuitable electrical stimulation to the heart of the patient. It iscontemplated that the communication pathway 308 may communicate using RFsignals, inductive coupling, optical signals, acoustic signals, or anyother signals suitable for communication. Additionally, in at least someexamples, device communication pathway 308 may include multiple signaltypes. For instance, other sensors/device 310 may communicate with theexternal device 306 using a first signal type (e.g. RF communication)but communicate with the LCPs 302/304 using a second signal type (e.g.conducted communication). Further, in some examples, communicationbetween devices may be limited. For instance, as described above, insome examples, the LCPs 302/304 may communicate with the external device306 only through other sensors/devices 310, where the LCPs 302/304 sendsignals to other sensors/devices 310, and other sensors/devices 310relay the received signals to the external device 306.

In some cases, the communication pathway 308 may include conductedcommunication. Accordingly, devices of the system 300 may havecomponents that allow for such conducted communication. For instance,the devices of system 300 may be configured to transmit conductedcommunication signals (e.g. current and/or voltage pulses) into thepatient's body via one or more electrodes of a transmitting device, andmay receive the conducted communication signals (e.g. pulses) via one ormore electrodes of a receiving device. The patient's body may “conduct”the conducted communication signals (e.g. pulses) from the one or moreelectrodes of the transmitting device to the electrodes of the receivingdevice in the system 300. In such examples, the delivered conductedcommunication signals (e.g. pulses) may differ from pacing or othertherapy signals. For example, the devices of the system 300 may deliverelectrical communication pulses at an amplitude /pulse width that issub-threshold to the heart. Although, in some cases, the amplitude/pulsewidth of the delivered electrical communication pulses may be above thecapture threshold of the heart, but may be delivered during a blankingperiod of the heart and/or may be incorporated in or modulated onto apacing pulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired.

FIG. 11 shows an illustrative medical device systems. In FIG. 11, an LCP402 is shown fixed to the interior of the left ventricle of the heart410, and a pulse generator 406 is shown coupled to a lead 412 having oneor more electrodes 408 a-408 c. In some cases, the pulse generator 406may be part of a subcutaneous implantable cardioverter-defibrillator(S-ICD), and the one or more electrodes 408 a-408 c may be positionedsubcutaneously. In some cases, the one or more electrodes 408 a-408 cmay be placed inside of the chest cavity but outside of the heart, suchas just interior of the sternum.

In some cases, the LCP 402 may communicate with the subcutaneousimplantable cardioverter-defibrillator (S-ICD). In some cases, the lead412 may include an accelerometer 414 that may, for example, beconfigured to sense vibrations that may be indicative of heart sounds.

In some cases, the LCP 402 may be in the right ventricle, right atrium,left ventricle or left atrium of the heart, as desired. In some cases,more than one LCP 402 may be implanted. For example, one LCP may beimplanted in the right ventricle and another may be implanted in theright atrium. In another example, one LCP may be implanted in the rightventricle and another may be implanted in the left ventricle. In yetanother example, one LCP may be implanted in each of the chambers of theheart.

When an LCP is placed in, for example, the left ventricle, and no LCP isplaced in the left atrium, techniques of the present disclosure may beused to help determine an atrial contraction timing fiducial for theleft atrium. This atrial contraction timing fiducial may then be used todetermine a proper time to pace the left ventricle via the LCP, such asan AV delay after the atrial contraction timing fiducial.

FIG. 12 is a side view of an illustrative implantable leadless cardiacpacemaker (LCP) 610. The LCP 610 may be similar in form and function tothe LCP 100 described above. The LCP 610 may include any of the modulesand/or structural features described above with respect to the LCP 100described above. The LCP 610 may include a shell or housing 612 having aproximal end 614 and a distal end 616. The illustrative LCP 610 includesa first electrode 620 secured relative to the housing 612 and positionedadjacent to the distal end 616 of the housing 612 and a second electrode622 secured relative to the housing 612 and positioned adjacent to theproximal end 614 of the housing 612. In some cases, the housing 612 mayinclude a conductive material and may be insulated along a portion ofits length. A section along the proximal end 614 may be free ofinsulation so as to define the second electrode 622. The electrodes 620,622 may be sensing and/or pacing electrodes to provide electro-therapyand/or sensing capabilities. The first electrode 620 may be capable ofbeing positioned against or may otherwise contact the cardiac tissue ofthe heart while the second electrode 622 may be spaced away from thefirst electrode 620. The first and/or second electrodes 620, 622 may beexposed to the environment outside the housing 612 (e.g. to blood and/ortissue).

In some cases, the LCP 610 may include a pulse generator (e.g.,electrical circuitry) and a power source (e.g., a battery) within thehousing 612 to provide electrical signals to the electrodes 620, 622 tocontrol the pacing/sensing electrodes 620, 622. While not explicitlyshown, the LCP 610 may also include, a communications module, anelectrical sensing module, a mechanical sensing module, and/or aprocessing module, and the associated circuitry, similar in form andfunction to the modules 102, 106, 108, 110 described above. The variousmodules and electrical circuitry may be disposed within the housing 612.Electrical communication between the pulse generator and the electrodes620, 622 may provide electrical stimulation to heart tissue and/or sensea physiological condition.

In the example shown, the LCP 610 includes a fixation mechanism 624proximate the distal end 616 of the housing 612. The fixation mechanism624 is configured to attach the LCP 610 to a wall of the heart H, orotherwise anchor the LCP 610 to the anatomy of the patient. In someinstances, the fixation mechanism 624 may include one or more, or aplurality of hooks or tines 626 anchored into the cardiac tissue of theheart H to attach the LCP 610 to a tissue wall. In other instances, thefixation mechanism 624 may include one or more, or a plurality ofpassive tines, configured to entangle with trabeculae within the chamberof the heart H and/or a helical fixation anchor configured to be screwedinto a tissue wall to anchor the LCP 610 to the heart H. These are justexamples.

The LCP 610 may further include a docking member 630 proximate theproximal end 614 of the housing 612. The docking member 630 may beconfigured to facilitate delivery and/or retrieval of the LCP 610. Forexample, the docking member 630 may extend from the proximal end 614 ofthe housing 612 along a longitudinal axis of the housing 612. Thedocking member 630 may include a head portion 632 and a neck portion 634extending between the housing 612 and the head portion 632. The headportion 632 may be an enlarged portion relative to the neck portion 634.For example, the head portion 632 may have a radial dimension from thelongitudinal axis of the LCP 610 that is greater than a radial dimensionof the neck portion 634 from the longitudinal axis of the LCP 610. Insome cases, the docking member 630 may further include a tetherretention structure 636 extending from or recessed within the headportion 632. The tether retention structure 636 may define an opening638 configured to receive a tether or other anchoring mechanismtherethrough. While the retention structure 636 is shown as having agenerally “U-shaped” configuration, the retention structure 636 may takeany shape that provides an enclosed perimeter surrounding the opening638 such that a tether may be securably and releasably passed (e.g.looped) through the opening 638. In some cases, the retention structure636 may extend though the head portion 632, along the neck portion 634,and to or into the proximal end 614 of the housing 612. The dockingmember 630 may be configured to facilitate delivery of the LCP 610 tothe intracardiac site and/or retrieval of the LCP 610 from theintracardiac site. While this describes one example docking member 630,it is contemplated that the docking member 630, when provided, can haveany suitable configuration.

It is contemplated that the LCP 610 may include one or more pressuresensors 640 coupled to or formed within the housing 612 such that thepressure sensor(s) is exposed to the environment outside the housing 612to measure blood pressure within the heart. For example, if the LCP 610is placed in the left ventricle, the pressure sensor(s) 640 may measurethe pressure within the left ventricle. If the LCP 610 is placed inanother portion of the heart (such as one of the atriums or the rightventricle), the pressures sensor(s) may measure the pressure within thatportion of the heart. The pressure sensor(s) 640 may include a MEMSdevice, such as a MEMS device with a pressure diaphragm andpiezoresistors on the diaphragm, a piezoelectric sensor, acapacitor-Micro-machined Ultrasonic Transducer (cMUT), a condenser, amicro-monometer, or any other suitable sensor adapted for measuringcardiac pressure. The pressures sensor(s) 640 may be part of amechanical sensing module described herein. It is contemplated that thepressure measurements obtained from the pressures sensor(s) 640 may beused to generate a pressure curve over cardiac cycles. The pressurereadings may be taken in combination with impedance measurements (e.g.the impedance between electrodes 620 and 622) to generate apressure-impedance loop for one or more cardiac cycles as will bedescribed in more detail below. The impedance may be a surrogate forchamber volume, and thus the pressure-impedance loop may berepresentative for a pressure-volume loop for the heart H.

In some embodiments, the LCP 610 may be configured to measure impedancebetween the electrodes 620, 622. More generally, the impedance may bemeasured between other electrode pairs, such as the additionalelectrodes 114′ described above. In some cases, the impedance may bemeasure between two spaced LCP's, such as two LCP's implanted within thesame chamber (e.g. LV) of the heart H, or two LCP's implanted indifferent chambers of the heart H (e.g. RV and LV). The processingmodule of the LCP 610 and/or external support devices may derive ameasure of cardiac volume from intracardiac impedance measurements madebetween the electrodes 620, 622 (or other electrodes). Primarily due tothe difference in the resistivity of blood and the resistivity of thecardiac tissue of the heart H, the impedance measurement may vary duringa cardiac cycle as the volume of blood (and thus the volume of thechamber) surrounding the LCP changes. In some cases, the measure ofcardiac volume may be a relative measure, rather than an actual measure.In some cases, the intracardiac impedance may be correlated to an actualmeasure of cardiac volume via a calibration process, sometimes performedduring implantation of the LCP(s). During the calibration process, theactual cardiac volume may be determined using fluoroscopy or the like,and the measured impedance may be correlated to the actual cardiacvolume.

In some cases, the LCP 610 may be provided with energy deliverycircuitry operatively coupled to the first electrode 620 and the secondelectrode 622 for causing a current to flow between the first electrode620 and the second electrode 622 in order to determine the impedancebetween the two electrodes 620, 622 (or other electrode pair). It iscontemplated that the energy delivery circuitry may also be configuredto deliver pacing pulses via the first and/or second electrodes 620,622. The LCP 610 may further include detection circuitry operativelycoupled to the first electrode 620 and the second electrode 622 fordetecting an electrical signal received between the first electrode 620and the second electrode 622. In some instances, the detection circuitrymay be configured to detect cardiac signals received between the firstelectrode 620 and the second electrode 622.

When the energy delivery circuitry delivers a current between the firstelectrode 620 and the second electrode 622, the detection circuitry maymeasure a resulting voltage between the first electrode 620 and thesecond electrode 622 (or between a third and fourth electrode separatefrom the first electrode 620 and the second electrode 622) to determinethe impedance. When the energy delivery circuitry delivers a voltagebetween the first electrode 620 and the second electrode 622, thedetection circuitry may measure a resulting current between the firstelectrode 620 and the second electrode 622 (or between a third andfourth electrode separate from the first electrode 620 and the secondelectrode 622) to determine the impedance.

In some instances, the impedance may be measured between electrodes ondifferent devices and/or in different heart chambers. For example,impedance may be measured between a first electrode in the leftventricle and a second electrode in the right ventricle. In anotherexample, impedance may be measured between a first electrode of a firstLCP in the left ventricle and a second LCP in the left ventricle. In yetanother example, impedance may be measured from an injected current. Forexample, a medical device (such as, but not limited to an SICD such asthe SICD 12 of FIG. 1), may inject a known current into the heart andthe LCP implanted in the heart H may measure a voltage resulting fromthe injected current to determine the impedance. These are just someexamples.

FIG. 13 is a flow diagram showing a method 700 for regulating apatient's heart using the medical system 10 (FIG. 1) including the SICD12 and the LCP 14. As seen generally at block 702, the SICD 12 may beused in a chronic monitoring mode in which the SICD 12 monitors acardiac EGM for indications of a possible arrhythmia. An acute mode maybe activated if the SICD 12 identifies a possible arrhythmia, and theLCP 14 may be instructed to help confirm the possible arrhythmia usingthe LCP electrodes and/or at least one of the one or more additionalsensors of the LCP as noted at block 704. If the possible arrhythmia isconfirmed (e.g. by the LCP or SICD), and if the possible arrhythmia isdangerous, the SICD 12 may deliver shock therapy to the heart via theelectrodes of the SICD 12, as seen at block 706. As indicated at block708, if the possible arrhythmia is confirmed and is not dangerous,inhibiting delivery of shock therapy to the heart via the electrodes ofthe SICD 12 and continuing in the acute mode in which the LCP electrodesand/or the at least one of the one or more additional sensors of the LCPare used to monitor cardiac activity. As noted at block 710, if thepossible arrhythmia is not confirmed, the SICD 12 may inhibit deliveryof shock therapy to the heart and may continue in the acute mode inwhich the LCP electrodes and/or the at least one of the one or moreadditional sensors of the LCP 14 are used to monitor cardiac activity.In some cases, as seen at block 710, if the possible arrhythmia is notconfirmed, the SICD 12 may instead deliver shock therapy. In some cases,this is a programmable setting that a physician may select for aparticular patient. For some patients, the SICD 12 may be programmed toinhibit shock therapy when the LCP 14 is either unable to confirm thepossible arrhythmia or if communication with the LCP 14 fails. For otherpatients, the SICD 12 may be programmed to deliver a shock in thesesituations. In some cases, and as indicated at optional block 712, theSICD 12 may return to the chronic monitoring mode once the possiblearrhythmia has terminated.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of thedisclosure. This may include, to the extent that it is appropriate, theuse of any of the features of one example embodiment being used in otherembodiments.

What is claimed is:
 1. A medical system for sensing and regulatingcardiac activity of a patient, the medical system comprising: acardioverter configured to generate and deliver shocks to cardiactissue; a leadless cardiac pacemaker (LCP) configured to sense cardiacactivity, the LCP configured to communicate with the cardioverter; thecardioverter configured to detect a possible arrhythmia; upon detectingthe possible arrhythmia, the cardioverter is configured to send averification request to the LCP soliciting verification from the LCPthat the possible arrhythmia is occurring; upon receiving theverification request from the cardioverter, the LCP is configured to usesignals from one or more of a plurality of sensors of the LCP to attemptto confirm that the possible arrhythmia is occurring; the LCP is furtherconfigured to send a confirmation response to the cardioverter if theLCP confirms that the possible arrhythmia is occurring; the cardioverteris configured to generate and deliver a therapy to cardiac tissue if theLCP confirms that the possible arrhythmia is occurring; and thecardioverter is configured to inhibit delivery of a therapy to cardiactissue if the LCP did not confirm that the possible arrhythmia isoccurring.
 2. The medical system of claim 1, wherein: at least some ofthe plurality of sensors of the LCP comprise: a first sensor that whenactivated consumes a first level of power; a second sensor that whenactivated consumes a second level of power, wherein the second level ofpower is higher than the first level of power; upon receiving theverification request from the cardioverter, the LCP is configured toinitially activate the first sensor to attempt to confirm that thepossible arrhythmia is occurring; if the LCP confirms that the possiblearrhythmia is occurring using the first sensor, the LCP is configured tosend the confirmation response to the cardioverter; if the LCP does notconfirm that the possible arrhythmia is occurring using the firstsensor, the LCP is configured to activate the second sensor to attemptto confirm that the possible arrhythmia is occurring; and if the LCPconfirms that the possible arrhythmia is occurring using the secondsensor, the LCP is configured to send the confirmation response to thecardioverter.
 3. The medical system of claim 2, wherein: the LCP furthercomprises a third sensor that when activated consumes a third level ofpower, wherein the third level of power is higher than the second levelof power; if the LCP does not confirm that the possible arrhythmia isoccurring using the second sensor, the LCP is configured to activate thethird sensor to attempt to confirm that the possible arrhythmia isoccurring; and if the LCP confirms that the possible arrhythmia isoccurring using the third sensor, the LCP is configured to send theconfirmation response to the cardioverter.
 4. The medical system ofclaim 2, wherein the LCP comprises at least a first electrode and asecond electrode, and the first sensor comprises detecting electricalcardiac activity via the first electrode and the second electrode. 5.The medical system of claim 4, wherein the second sensor is configuredto detect heart sounds.
 6. The medical system of claim 4, wherein thesecond sensor comprises an accelerometer disposed relative to the LCP.7. The medical system of claim 4, wherein the second sensor comprises apressure sensor disposed relative to the LCP.
 8. The medical system ofclaim 3, wherein the third sensor comprises an optical sensor.
 9. Themedical system of claim 1, wherein the verification request from theimplantable cardioverter includes an indication of severity of thepossible arrhythmia, and if the indication of severity exceeds athreshold severity level, the LCP is configured to concurrently activatetwo or more of the plurality of sensors and to use the concurrentlyactivated two or more of the plurality of sensors to attempt to confirmthat the possible arrhythmia is occurring in an expedited manner. 10.The medical system of claim 1, wherein the LCP is configured toconcurrently activate two of the plurality of sensors upon receiving theverification request from the cardioverter; and the LCP is configured toexamine a relationship between a signal from a first sensor of theplurality of sensors and a signal from a second sensor of the pluralityof sensors to attempt to confirm that the possible arrhythmia isoccurring.
 11. A leadless cardiac pacemaker (LCP) configured forimplantation relative to a patient's heart, the LCP configured to senseelectrical cardiac activity and to deliver pacing pulses whenappropriate, the LCP comprising: a housing; a first electrode securedrelative to the housing; a second electrode secured relative to thehousing, the second electrode spaced from the first electrode; acontroller disposed within the housing and operably coupled to the firstelectrode and the second electrode such that the controller is capableof receiving, via the first electrode and the second electrode,electrical cardiac signals of the heart, the first electrode and thesecond electrode comprising a first sensor that, when activated,consumes a first level of power; a second sensor disposed relative tothe housing and operably coupled to the controller, the second sensor,when activated, consumes a second level of power that is higher than thefirst level of power; a communications module disposed relative to thehousing and operably coupled to the controller, the communicationsmodule configured to receive a verification request from a cardioverterto confirm that a possible arrhythmia is occurring; upon receipt of theverification request from the cardioverter via the communicationsmodule, the controller is configured to initially sense cardiac activityusing the first sensor to help confirm that the possible arrhythmia isoccurring while the second sensor is in a lower power state; and if thepossible arrhythmia is not confirmed using the first sensor, thecontroller is configured to activate the second sensor from the lowerpower state to a higher power state, and then sense cardiac activityusing the second sensor to help confirm that the possible arrhythmia isoccurring.
 12. The LCP of claim 11, wherein the second sensor comprisesan accelerometer or a pressure sensor.
 13. The LCP of claim 11, furthercomprising: a third sensor disposed relative to the housing and operablycoupled to the controller, the third sensor, when activated, consumes athird level of power that is higher than the second level of power; ifthe possible arrhythmia is not confirmed using the second sensor, thecontroller is configured to activate the third sensor from the lowerpower state to a higher power state, and then attempt to confirm thatthe possible arrhythmia is occurring using the third sensor; and if thepossible arrhythmia is confirmed using the third sensor, the controlleris configured to send the confirmation response to the cardioverter viacommunications module confirming that the possible arrhythmia isoccurring.
 14. The LCP of claim 13, wherein the second sensor comprisesan accelerometer, and the third sensor comprises a pressure sensor or anoptical sensor.
 15. The LCP of claim 11, wherein the verificationrequest from the cardioverter includes an indication of severity of thepossible arrhythmia, and if the indication of severity exceeds athreshold severity level, the controller is configured to concurrentlyactivate the first sensor and the second sensor in order to more quicklyconfirm or deny the possible arrhythmia.
 16. The LCP of claim 15,wherein the cardioverter is configured to examine a relationship betweena signal from the first sensor and a signal from the second sensor toattempt to confirm that the possible arrhythmia is occurring.
 17. TheLCP of claim 11, wherein if the possible arrhythmia is not confirmedusing the first sensor, the controller is configured to activate thefirst sensor and the second sensor and to send a signal to theimplantable cardioverter so that the implantable cardioverter canexamine a relationship between a signal from the first sensor and asignal from the second sensor to attempt to confirm that the possiblearrhythmia is occurring.
 18. A method of regulating a patient's heartusing a medical system including a cardioverter and a leadless cardiacpacemaker (LCP), the cardioverter configured to monitor a cardiac EGMvia electrodes disposed on an electrode support and deliver shocktherapy via the electrodes, the LCP configured to sense electricalcardiac activity via LCP electrodes disposed on the LCP, the LCPincluding one or more additional sensors, the method comprising: usingthe cardioverter in a chronic monitoring mode, the cardiovertermonitoring the cardiac EGM for indications of a possible arrhythmia;activating an acute mode if the cardioverter identifies a possiblearrhythmia, and instructing the LCP to help confirm the possiblearrhythmia using the LCP electrodes and/or at least one of the one ormore additional sensors of the LCP; if the possible arrhythmia isconfirmed, and if the possible arrhythmia is dangerous, delivering shocktherapy to the heart via the electrodes of the cardioverter; if thepossible arrhythmia is confirmed and is not dangerous, inhibitingdelivery of shock therapy to the heart via the electrodes of thecardioverter and continuing in the acute mode in which the LCPelectrodes and/or the at least one of the one or more additional sensorsof the LCP are used to monitor cardiac activity; and if the possiblearrhythmia is not confirmed, inhibiting delivery of shock therapy to theheart via the electrodes of the cardioverter and continuing in the acutemode in which the LCP electrodes and/or the at least one of the one ormore additional sensors of the LCP are used to monitor cardiac activity.19. The method of claim 18, further comprising returning to the chronicmonitoring mode once the possible arrhythmia has terminated.
 20. Themethod of claim 18, wherein the one or more additional sensors compriseone or more of an accelerometer, a pressure sensor, and an opticalsensor.